Hi Showard,
Are you refering to colours on your screen that are printing out darker? The colours that appear on your screen are displayed using a different colour system and light source than those on a printed page, so naturally they will print darker.
If you mean the colours print out darker on press than from the proofing device you're using, then I suspect it is a colour management issue. Have you asked your printer for a color profile? Each time you use a different output device, you should apply a color profile that is calibrated for that device (printer).
I could explain this in more detail, but it might be easier to order my book,
Exploring Digital Prepresswww.amazon.ca/gp/product/141801236X/701-0065180-5101126If you want to get seriously into colour management, here is another good resource:
Abay Sharma -
Understanding Color Management